Molecular epidemiology of emerging begomovirus diseases on vegetable crops in Burkina Faso. [O21]

Background and objectives begomoviruses (family geminiviridea) are transmitted by Bemisia tabaci and are responsible for serious diseases in the world. African begomoviruses described on crops are mainly monopartite (dna-a component), except cassava-infecting bipartite begomoviruses (dna-a and dna-b components). In recent years, a complex of more than 10 monopartite begomoviruses responsible for tomato (yellow) leaf curldiseases (tylcd-tolcd) has been described on tomato in sub-Saharan Africa [1]. Faced with the upsurge of vegetable virus diseasesin Burkina Faso, we have undertaken (1) to identify the causal agents and their molecular diversity, and (2) to investigate their main epidemiological parameters in the field and under controlled conditions. Material and methods forty-five localities from the main vegetable-growing areas of Burkina Faso were surveyed from 2013 to 2016. In total, 2065 leaf samples were collected from cultivated and uncultivated plants. Some of them were subjected to begomovirusdiagnosis (sequence-dependent methods) by pcr, rolling circle amplification, cloning and sequencing and others were used for more accurate and complete description of virus communities using a metagenomicapproach (sequence-independent methods) based on rca, pcr-random amplification tagging and illumina sequencing. Agroinfectious clones were constructed in order to assess the pathogenicity of some characterized viruses. The transmission rate of these viruses was estimated after acquisition of the virus by B. tabaci. Results we have cloned and sequenced 143 dna sequences (109 dna-a and 34 dna-b). Nucleotide similarity analyses confirmed the presence of at least four known African monopartite begomoviruses (clcugv, pepyvmv, tolmlv and tolcghv). It also revealed for the first time in West Africa the mastreviruscpcdv on tomato and a new species named“tomato leaf curlBurkina Faso virus”. We characterized a dna-b molecule on cultivated and uncultivated plants, unexpectedly always associated with the dna-a of pepyvmv, which is distantly related to the known dna-b diversity. In addition to the previous five geminiviruses, the metagenomicapproach suggested the presence of at least five other viruses. Our agroinoculation tests demonstrate that the sole pepyvmv dna-a does not induce tylcd-tolcd symptoms on tomato in experimental conditions. However, in coinfection dna-b is an activator of the virulence of the cognate pepyvmv dna-a. Conclusions our work suggest that tylcd-tolcd in Burkina Faso is associated with a complex of geminiviruses and that sequence-independent deep sequencingbased approaches are interesting and complementary to further study the diversity of plant viruses. We demonstrate experimentally that the newly characterized dna-b component represents a major pathogenity activator for pepyvmv dna-a. Our first investigations may suggest that this dna-b component recruited by pepyvmv dna-a could be the main epidemiological factor for the emergence of pepyvmv as the most prevalent and severe plant virusdisease on tomato and pepper in Burkina Faso. (Resume d'auteur)